The major focus of this proposal is to determine if co-expression and subsequent formation of "mixed" heterogeneous gap junction channels represents a unique pathway for the regulation of intercellular communication. The PI will study subunit connexin co-expression of Cx45, Cx43, and Cx40 in vitro. All are connexins found in specialized cardiac tissue and are thought to be critical to normal and abnormal cardiac rhythm, for example. Two experimental approaches will be used to assess the presence of heterogeneous channels. First dual whole cell patch clamp and extensive analysis of channel properties will be initiated. Second a connexin transgene expression system will be used to regulate the amount of each connexin produced. The PI will monitor/utilize phosphorylation as a tool to demonstrate if "mixed" channels (heteromeric, mono-heteromeric) gate or have unitary conductances which are significantly different from homotypic channel types.